Stable breaker-crosslinker-polymer complex and method of use in completion and stimulation

ABSTRACT

A preferred novel breaker-crosslinker-polymer complex and a method for using the complex in a fracturing fluid to fracture a subterranean formation that surrounds a well bore by pumping the fluid to a desired location within the well bore under sufficient pressure to fracture the surrounding subterranean formation. The complex may be maintained in a substantially non-reactive state by maintaining specific conditions of pH and temperature, until a time at which the fluid is in place in the well bore and the desired fracture is completed. Once the fracture is completed, the specific conditions at which the complex is inactive are no longer maintained. When the conditions change sufficiently, the complex becomes active and the breaker begins to catalyze polymer degradation causing the fracturing fluid to become sufficiently fluid to be pumped from the subterranean formation to the well surface.

BACKGROUND OF THE INVENTION

Oil well stimulation typically involves injecting a fracturing fluidinto the well bore at extremely high pressure to create fractures in therock formation surrounding the bore. The fractures radiate outwardlyfrom the well bore, typically from about 100 to 1000 meters, and extendthe surface area from which oil or gas drains into the well. Thefracturing fluid typically carries a propping agent, or "proppant," suchas sand, so that the fractures are propped open when the pressure on thefracturing fluid is released, and the fracture closes around thepropping agent.

Fracturing fluid typically contains a water soluble polymer, such asguar gum or a derivative thereof, that provides appropriate flowcharacteristics to the fluid and suspends the proppant particle. Whenpressure on the fracturing fluid is released and the fracture closesaround the propping agent, water is forced out and the water-solublepolymer forms a filter cake. This filter cake can prevent oil or gasflow if it is not removed.

Breakers are added to the fracturing fluid to enable removal of thefilter cake. Breakers catalyze the breakdown of the polymer in thecompacted cake to simple sugars, making the polymer fluid so that it canbe pumped out of the well. Currently, breakers are either enzymaticbreakers or oxidative breakers.

Oxidative breakers have been widely applied in fracturing applications.Oxidizers react non-specifically with any oxidizable material includinghydrocarbons, tubular goods, formation components, and other organicadditives. Oxidizers release free radicals that react upon susceptibleoxidizable bonds or sites. Free radicals are charged ions with unpairedelectrons and are very reactive due to their natural tendency to formelectron-pair bonds. Free radicals can be generated from either thermalor catalytic activation of stable oxidative species. The major problemwith using oxidative breakers to remove a proppant cake is thatreactions involving free radicals are usually very rapid so the proppantcake may become fluid before the pumping treatment is completed.

Encapsulated oxidative breakers were introduced to provide a delayedrelease of the persulfate breaker payload until after the pumpingtreatment is complete. However, there are several problems related tousing encapsulated breakers in hydraulic fracturing treatments. First,premature release of the oxidative payload sometimes occurs due toproduct manufacturing imperfections or coating damage resulting fromabrasion experienced in pumping the particles through surface equipment,tubulars, and perforations. Second, homogeneous distribution ofencapsulated breaker is more difficult within the propped fracture.Since the persulfate is confined to individual encapsulated particles,encapsulated breakers must be added throughout the pumping process toachieve adequate distribution.

Enzymes are a second type of breaker that exhibits a unique ability toact as a biocatalyst to accelerate chemical reactions. The catalyticactivity does not change the enzyme structure during reaction initiationand thus, the enzyme may initiate another reaction, and so on. Apolymer-specific enzyme is an enzyme that will align and react with onlythat particular polymer.

The problem with enzymatic breakers is that they begin catalyzingpolymer degradation immediately upon addition. Encapsulating enzymeshelps alleviate this problem, but causes the same type of problemsdescribed above with encapsulated oxidants. A method is needed toprevent or reduce immediate degradation of enzyme additives, whileallowing the enzymes to be evenly dispersed throughout the polymer andto retain their activity.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a gellable fracturing fluidcomposed of a breaker-crosslinker-polymer complex is provided. Thecomplex comprises a matrix of compounds, substantially all of whichinclude a breaker component, a crosslinker component and a polymercomponent. The complex may be maintained in a substantially non-reactivestate by maintaining specific conditions of pH and temperature. Apreferred breaker includes an enzyme more particularly ahigh-temperature-high-pH-guar-specific enzyme or ahigh-temperature-high-pH-cellulose specific enzyme. The preferredcrosslinker components include any of the conventionally usedcrosslinking agents that are known to those skilled in the art. Forinstance, in recent years, gellation of the hydratable polymer has beenachieved by crosslinking these polymers with metal ions includingaluminum, antimony, zirconium and titanium containing compoundsincluding the so-called organometallics. Transition metals such aszirconium and titanium crosslinkers are preferred. Borate ion donatingmaterials are also preferred as crosslinkers, for example, the alkalimetal and the alkaline earth metal borates and boric acid. Crosslinkersthat contain boron ion donating materials may be called borate systems.Crosslinkers that contain zirconium may be called zirconate systems. Apreferred polymer component includes guar or guar derivatives inparticular carboxymethyl-hydroxypropyl guar and cellulose or cellulosederivatives. The polymer must be compatible with the enzyme and thecrosslinker. The conditions at which a preferred complex may bemaintained in a substantially non-reactive state are about pH 9.3 to11.0 and temperature of about 70° F. to 300° F.

According to another aspect of the invention, a method for using thebreaker-crosslinker-polymer complex in gellable fracturing fluid areprovided. A preferred method for using the fracturing fluid includespumping the fluid comprising the complex in a substantially non-reactivestate to a desired location within the well bore under sufficientpressure to fracture the surrounding subterranean formation. The complexis then maintained in the substantially non-reactive state bymaintaining specific conditions of pH and temperature until a time atwhich the fluid is in place in the well bore and the desired fracturetreatment or operation is completed. Once the fracture is completed, thespecific conditions at which the complex is inactive are no longerrequired. Such conditions that may change, for example, are pH andtemperature. When the conditions change sufficiently, the complexbecomes active and the breaker begins to catalyze polymer degradationcausing the fluid to become less viscous, allowing the "broken" fluid tobe produced from the subterranean formation to the well surface. A"broken" fluid is considered as a fluid having a viscosity of less than10 cps at 511^(S-1).

The benefits of using the complex and the method of this invention arethat more even distribution of the breaker is achieved, initial orfront-end viscosity at temperature of the fracturing fluid issubstantially increased, and the filter cake is more efficientlyremoved. The benefits of this invention may be achieved when the breakeris added to a crosslinker and polymer combination or when the breaker isfirst combined with the crosslinker and then added to the polymer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In practicing a preferred method of the invention, an aqueous fracturingfluid is first prepared by blending a hydratable polymer into an aqueousfluid. The aqueous fluid could be, for example, water, brine, aqueousbased foams or water-alcohol mixtures. Any suitable mixing apparatus maybe used for this procedure. In the case of batch mixing, the hydratablepolymer and the aqueous fluid are blended for a period of timesufficient to form a hydrated solution. The hydratable polymers usefulin the present invention may be any of the hydratable polysaccharidesand are familiar to those in the well service industry. Thesepolysaccharides are capable of gelling in the presence of a crosslinkingagent to form a gelled based fluid. Specific examples are guar gum, guargum derivatives, cellulose and cellulose derivatives. The preferredgelling agents are guar gum, hydroxy propyl guar andcarboxymethyl-hydroxypropyl guar (CMHPG), carboxymethyl guar (CMG), orcarboxymethylhydroxy-ethyl cellulose (CMHEC).

The hydratable polymer may be added to the aqueous fluid inconcentrations ranging from about 0.06% to 1.8% by weight of the aqueousfluid. The most preferred range for the present invention is about 0.3%to about 0.96% by weight.

In addition to the hydratable polymer, the fracturing fluids of theinvention include a crosslinking agent. The preferred crosslinkersinclude any of the conventionally used crosslinking agents that areknown to those skilled in the art. For instance, in recent years,gellation of the hydratable polymer has been achieved by crosslinkingthese polymers with metal ions including aluminum, antimony, zirconiumand titanium containing compounds including the so-calledorganometallics. Transition metals such as zirconium and titaniumcrosslinkers are preferred. Borate ion donating materials are alsopreferred as crosslinkers, for example, the alkali metal and thealkaline earth metal borates and boric acid. See, for instance, U.S.Pat. No. 4,514,309 and U.S. Pat. No. 5,201,370. Zirconium and boroncrosslinking agents (zirconate or borate crosslinkers) are the mostpreferred of this invention.

A preferred zirconate crosslinking additive is preferably present in therange from about 0.5% to in excess of 2.0% by weight of the polymer.Preferably, the concentration of crosslinking agent is in the range fromabout 0.7% to about 1.5% by weight of the polymer.

A preferred borate crosslinking additive is preferably present in therange from about 0.5% to in excess of 2.0% by weight of the polymer.Preferably, the concentration of crosslinking agent is in the range fromabout 0.7% to about 1.5% by weight of the polymer.

Propping agents are typically added to the base fluid prior to theaddition of the crosslinking agent. Propping agents include, forinstance, quartz sand grains, glass and resin coated ceramic beads,walnut shell fragments, aluminum pellets, nylon pellets, and the like.The propping agents are normally used in concentrations between about 1to 18 pounds per gallon of fracturing fluid composition, but higher orlower concentrations can be used as required. The base fluid can alsocontain other conventional additives common to the well service industrysuch as surfactants.

Unlike the breaker system of the prior art, a new highly stablebreaker-crosslinker-polymer complex has been developed that reducespremature fluid degradation while allowing the breaker to be evenlydispersed throughout the polymer. Such a stablebreaker-crosslinker-polymer complex may be prepared by determiningspecific conditions of pH and temperature at which a specificbreaker-crosslinker-polymer forms a stable complex with a matrix ofcompounds, each compound including a compatible breaker, polymer, andcrosslinker. Then, fracturing fluid is maintained at those conditionsuntil the fluid is in place in the subterranean formation. Next, theconditions are allowed to vary such that the complex becomes active andthe reaction, in which the polymer is broken down to lower molecularweight fragments, is catalyzed by the breaker. Once the polymer isbroken down to lower molecular weight fragments, a fluid consistencydevelops that allows the polymer to be easily removed from the well.

Incredible unexpected rheological properties have been attributed to theuse of this breaker-crosslinker-polymer complex. Upon formation of thecomplex, up to about 50% increase in initial viscosity has beendemonstrated when compared to the initial viscosity of fracturing fluidswithout the complex to which breaker has been added. Tables 2 and 3demonstrate the high initial viscosity of this invention. This highinitial viscosity is believed to be due to a matrix of high molecularweight compounds contained in the complex. It is believed that each ofthe compounds in the matrix is made up of enzyme, crosslinker andpolymer held together in equilibrium as long as specific conditions aremaintained.

Preferred breaker components of this invention are polymer specificenzymes. A particularly advantageous feature of polymer-specific-enzymebreakers with respect to fracturing applications, is that uponintroduction to the aqueous polymer solution, the enzyme will attach toa strand of polymer. The enzyme will then "piggy-back" (bind or stayattached) on that polymer strand until such time as conditions areappropriate for the reaction to occur that completely degrades thepolymer. The enzyme will migrate to wherever the polymer travels; i.e.,within the primary fracture, into natural fractures, or into highpermeability matrices. Thus, the enzyme degradant will be distributedand concentrated homogeneously with the polymer throughout the fracture.

Preferred embodiments of the breaker-crosslinker-polymer complex havebeen demonstrated at a temperature range of about 70° F. to about 275°F. and at a pH of about 9.3 to about 10.5. In this environment,preferred breaker-crosslinker-polymer complexes remain in equilibriumwith very little or no dissociation and the breaker does notsubstantially degrade the polymer.

As can be seen in Tables 2 and 3, incredible initial viscosity has beendemonstrated with the breaker complex comprising ahigh-temperature-high-pH-guar-specific enzyme, a diesel slurried CMHPGand a zirconate or guar and a borate crosslinker, respectively. Insteadof the usual reduction in viscosity of up to 20% on addition of thebreaker, fracturing fluids including the breaker system of thisembodiment have exhibited substantially increased viscosity uponaddition of the breaker as may be seen by the immediate increase inviscosity demonstrated in Tables 1 and 2. This incredible initialviscosity has been demonstrated whether the enzyme was added to thecrosslinker and substrate or the enzyme and crosslinker were added tothe substrate.

The underlying basis of this invention may be better explained byconsidering conventional enzyme pathways which may be described by thefollowing reaction:

    E+S∴ ES!∴E+P                               (1)

in which E is an enzyme, S is a substrate, ES! is an intermediateenzyme-substrate complex and P is the product of the substratedegradation catalyzed by the enzyme. The reaction rate of theintermediate enzyme-substrate complex is pH dependent and may be slowedor even virtually halted by controlling the pH and temperature of theenzyme substrate complex.

Further explanation may be found in the following equations andexplanation from Malcom Dixon and Edwin C. Webb. Enzymes, AcademicPress, p. 162 (New York 1979). For an explanation of the abbreviations,see Table 1.

                  TABLE 1                                                         ______________________________________                                        SYMBOLS & ABBREVIATIONS                                                       SYMBOL or                                                                     ABBREVIATION                                                                             DEFINITION                                                         ______________________________________                                        S          Substrate                                                          ES         Enzyme-Substrate Complex                                           E          Enzyme                                                             P          Product                                                            E.sup.n    Enzyme with n negative charge                                      E.sup.n S  Enzyme (with n negative charge) - Substrate                                   Complex                                                            E.sup.n S' Enzyme (with n negative charge) - Substrate                                   (Intermediate)                                                                Complex prior to breakdown into Product (P)                        E.sup.n+1  Enzyme with n + 1 negative charge                                  E.sup.n+1 S                                                                              Enzyme with n + 1 negative charge - Substrate                                 Complex                                                            E.sup.n+1 S'                                                                             Enzyme with n + 1 negative charge - Substrate                                 (Intermediate)                                                                Complex prior to breakdown into Product (P)                        k.sub.+1, k.sub.+2, k.sub.+3                                                             Velocity constants of successive forward steps in an                          enzyme reaction                                                    K          Overall equilibrium constant between E.sup.n S and E.sup.n S'      K'         Overall equilibrium constant between E.sup.n+1 S and                          E.sup.n+1 S'                                                       K.sup.S.sub.s                                                                            Apparent dissociation constant of E.sup.n S Complex                K.sup.S.sub.s'                                                                           Apparent dissociation constant of E.sup.n+1 S Complex              K.sub.e, K.sub.es, K.sub.es'                                                             Ionization constants of E.sup.n,, E.sup.n S, E.sup.n S'                       respectively                                                       ______________________________________                                    

Some researchers term such an enzyme-substrate complex that has beenvirtually halted, a non-productive complex. If a substrate forms anon-productive complex with an enzyme, the pH dependence of V and K_(m)may give an apparent pK value which diverges from the real value in theproductive complex if the ratio of correct to abortive binding changeswith the pH. For the scheme: ##STR1## in which the breakdown of theE^(n) S complex is so slow that the remainder of the system remains inequilibrium, the rate equation becomes ##EQU1## and thus the observed pKvalue obtained from plots of pK_(m) or log V against pH will differ fromthe true value by the expression ##EQU2##

As explained in Enzymes at p. 162, other instances of non-productivebinding have been discussed. A breaker-crosslinker-polymer complex,however, has not heretofore been described as a component of fracturingfluids.

The following examples will illustrate the invention, but should not beconstrued to limit the scope thereof unless otherwise expressly noted.

Example 1

A solution containing 2% (w/w) potassium chloride and 10 milliliters ofdiesel slurried CMHPG polymer (equivalent to 40 pounds per 1000 gallons)was hydrated in one liter of tap water for about 30 minutes. Thesolution was divided into 250 ml. aliquots. An aliquot was mixed at 1500rpm to get a vortex. A solution containing 0.3125 ml. of 45% potassiumcarbonate solution and 0.3125 ml. of zirconate crosslinker was mixeduntil gelling was completed. Forty-six grams of sample solution wastransferred to a FANN model 50C with an R1-B5 rotor cup configuration ofrheological measurement at 250° F. No enzyme breaker was added to thesystem of this example. The results in Table 2, example 1, illustratethe effect of the crosslinker on the polymer at these specificconditions.

Example 2

A solution containing 2% (w/w) potassium chloride and 10 milliliters ofdiesel slurried CMHPG polymer (equivalent to 40 pounds per 1000 gallons)was hydrated in on liter of tap water for about 30 minutes. The solutionwas divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm toget a vortex. A solution containing 0.3125 ml. of 45% potassiumcarbonate solution, 0.25 ml. of high-temperature-high-pH-guar-specificenzyme with about 30,400 international enzyme units per gram, and 0.3125ml. of zirconate crosslinker was mixed until gelling was completed.Forty-six grams of sample solution was transferred to a FANN model 50Cwith an R-1-B5 rotor cup configuration for rheological measurement at250° F. The results in Table 2, example 2, illustrate the effect ofholding this particular fracturing fluid at a pH of about 9.3 and atemperature of 250° F. on the viscosity of the fracture fluid.

Example 3

A solution containing 2% (w/w) potassium chloride and 10 milliliters ofdiesel slurried CMHPG polymer (equivalent to 40 pounds per 1000 gallons)was hydrated in one liter of tap water for about 30 minutes. Thesolution was divided into 250 ml. aliquots. An aliquot was mixed at 1500rpm to get a vortex. A solution containing 0.3125 ml. of 45% potassiumcarbonate solution, 1.00 ml. of high-temperature-high-pH-guar-specificenzyme was mixed with about 30,400 international enzyme units per gram,and 0.3125 ml. of zirconate crosslinker were mixed until gelling wascompleted. Forty-six grams of sample solution was transferred to a FANNmodel 50C with an R1-B5 rotor cup configuration for rheologicalmeasurement at 250° F. The results in Table 2, example 3, illustrate theeffect of holding this particular fracturing fluid at a pH of about 9.3and a temperature of 250° F. on the viscosity of the fracture fluid.

Example 4

A solution containing 2% (w/w) potassium chloride and 10 milliliters ofdiesel slurried CMHPG polymer (equivalent to 40 pounds per 1000 gallons)was hydrated in one liter of tap water for about 30 minutes. Thesolution was divided into 250 ml. aliquots. An aliquot was mixed at 1500rpm to get a vortex. A solution containing 0.3125 ml. of 45% potassiumcarbonate solution and 0.3425 ml. of a composite mixture of a zirconatecrosslinker and high-temperature-high-pH-guar specific enzyme with about30,400 international enzyme units per gam and 0.3125 ml. zirconatecrosslinker was mixed until gelling was completed. Forty-six grams ofsample solution was transferred to a FANN model 50C with an R1-B5 rotorcup configuration for rheological measurement at 250° F. The results inTable 2, example 5, illustrate the effect of holding this particularfracturing fluid at a pH of about 9.3 and a temperature of 250° F. onthe viscosity of the fracturing fluid. These results demonstrate thatthe beneficial effects of increased viscosity of this fracturing fluidwas not affected by adding the crosslinker and the enzyme incombination.

                  TABLE 2                                                         ______________________________________                                        VISCOSITY AT 40 sec.sup.-1                                                    TIME AT                                                                              EXAMPLE    EXAMPLE   EXAMPLE  EXAMPLE                                  TEMP., 1          2         3        4                                        HOURS  (cps)      (cps)     (cps)    (cps)                                    ______________________________________                                        0      691        1048      726      1141                                     1      591        983       860      962                                      2      633        649       696      577                                      3      448        401       503      376                                      4      622        217       338      259                                      5      514        122       185      201                                      6      401         83       111      154                                      7      267         60        80      133                                      8      182         43        60      112                                      9      115         39        39       98                                      10      94         34        37       89                                      12      42         13        28       74                                      14      24         2         12       16                                      ______________________________________                                    

Example 5

A solution containing 2% (w/w) potassium chloride and 10 milliliters ofdiesel slurried guar polymer (equivalent to 40 pounds per 1000 gallons)was hydrated in one liter of tap water about 30 minutes. The solutionwas divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm toget a vortex. A solution containing 2.50 ml. of 45% potassium carbonatesolution and 1.50 ml. of borate crosslinker were added and the solutionmixed until gelling was completed. Forty-two grams of sample solutionwas a FANN model 50C with an R1-B1 rotor cup configuration forrheological measurement 250° F. The results in Table 3, example 5,illustrate the effect of the crosslinker on the polymer at thesespecific conditions.

Example 6

A solution containing 2% (w/w) potassium chloride and 10 milliliters ofdiesel slurried guar polymer (equivalent to 40 pounds per 1000 gallons)was hydrated in one liter of tap water for about 30 minutes. Thesolution was divided into 250 ml. aliquots. An aliquot was mixed at 1500rpm to get a vortex. A solution containing 250 ml. of 45% potassiumcarbonate solution, 1.50 ml. of borate crosslinker, 0.25 ml. ofhigh-temperature-high pH-guar-specific enzyme with about 30,400international enzyme units per gram was mixed until gelling wascompleted. Forty-two grams of sample solution was transferred to a FANNmodel 50C with an R1-B1 rotor cup configuration for rheologicalmeasurement at 250° F. The results in Table 3, example 6, illustrate theeffect of holding this particular fracturing fluid at a pH of about 10.3and a temperature of 250° F. on the viscosity of the fracturing fluid.

Example 7

A solution containing 2% (w/w) potassium chloride and 10 milliliters ofdiesel slurried guar polymer (equivalent to 40 pounds per 1000 gallons)was hydrated in one liter of tap water for about 30 minutes. Thesolution was divided into 250 ml. aliquots. An aliquot was mixed at 1500rpm to get a vortex. A solution containing 2.50 ml. of 45% potassiumcarbonate solution, 1.50 ml. of borate crosslinker and 1.0 ml. ofhigh-temperature-high-pH-guar-specific enzyme with about 30,400international enzyme units per gram was mixed until gelling wascompleted. Forty-two grams of sample solution was transferred to a FANNmodel 50C with an R1-B1 rotor cup configuration for rheologicalmeasurement at 250° F. The results in Table 3, example 7, illustrate theeffect of holding this particular fracturing fluid at a pH of about 10.3and a temperature of 250° F. on the viscosity of the fracturing fluid.

                  TABLE 3                                                         ______________________________________                                        TIME AT TEMP.,                                                                           VISCOSITY AT 40 SEC.sup.-1                                         HOURS      EXAMPLE 5  EXAMPLE 6   EXAMPLE 7                                   ______________________________________                                        0          1021       907         922                                         1          716        976         881                                         2          462        877         655                                         3          342        734         512                                         4          246        608         425                                         5          185        484         312                                         ______________________________________                                    

The preceding description of specific embodiments for the presentinvention is not intended to be a complete list of every embodiment ofthe invention. Persons who are skilled in this field will recognize thatmodifications can be made to the specific embodiments described hereinthat would be within the scope of the invention.

What is claimed is:
 1. A method of fracturing a subterranean formationthat surrounds a well bore comprising the steps of:forming a gellablefracturing fluid comprising the steps of:selecting a compatible polymer,crosslinker and breaker; and combining the breaker with the crosslinkerto form a breaker-crosslinker combination; forming a substantiallynon-reactive breaker-crosslinker-polymer complex by combining thebreaker-crosslinker combination with the polymer; and maintainingconditions sufficient to promote formation and maintenance of a stablebreaker-crosslinker-polymer complex, said breaker-crosslinker-polymercomplex further comprising a matrix of compounds, said compounds eachcomprising a breaker component, a crosslinker component and a polymercomponent; pumping the fracturing fluid to a desired location within thewell bore under sufficient pressure to fracture the surroundingsubterranean formations; ceasing to maintain thebreaker-crosslinker-polymer complex at conditions sufficient to maintainsaid substantially non-reactive complex, allowing polymer breakdown tobe catalyzed by said breaker, whereby the polymer becomes sufficientlyfluid to be pumped from the subterranean formation to the well surface.2. A method according to claim 1, comprising forming the substantiallynon-active breaker-crosslinker-polymer complex substantiallysimultaneously with pumping the fracturing fluid into the well.
 3. Amethod according to claim 1, wherein the breaker comprises an enzyme. 4.A method according to claim 3, wherein the crosslinker is selected fromthe group consisting of zirconium and a source of borate ions; theenzyme comprises a cellulose specific enzyme; and the polymer comprisesa cellulose or a cellulose derivative.
 5. A method according to claim 3,wherein the crosslinker comprises a borate system;the enzyme comprises aguar specific enzyme; and the polymer comprises a guar or a guarderivative.
 6. A method according to claim 3, wherein the crosslinkercomprises a transition metal.
 7. A method according to claim 1, whereinthe breaker comprises a cellulose-specific enzyme; the polymer comprisesa cellulose or a cellulose derivative; and the specific conditionselected to promote internal breaker-stabilizer-complex formationcomprises a pH of about 9.3 to about 10.5 and a temperature of about 70°F. to about 300° F.
 8. A method according to claim 1, wherein:thebreaker comprises a high-temperature-high-pH-guar-specific enzyme; thepolymer comprises a guar or a guar derivative; the crosslinker comprisesa transition metal; and the specific condition selected to promoteinternal breaker-stabilizer-complex formation comprises a pH of about9.3 to about 10.5 and a temperature of about 70° F. to about 300° F. 9.A method according to claim 1, wherein the polymer comprises a celluloseor a cellulose derivative and the breaker comprises ahigh-temperature-high-pH cellulose-specific enzyme; and the crosslinkercomprises a transition metal.